Roger Pielke Jr: Can you point to the specific work by Daniel Nepstad that justifies the IPCC claim that “40% of the Amazon forests could react drastically …”? I looked into this and found no such statements in any of Nepstad’s (or anyone else’s) work. You claim otherwise. What have I missed?

Pearce: Nepstad himself says the 40% claim is correct. He cites two of his own papers:

[Firstly, Nepstad (2004) and secondly… Nepstad (2007)].

The latter [Nepstad, 2007] found a “38% increase in mortality” from a simulated drought in a large-scale forest experiment. That seems reasonable justification for the “up to 40 per cent of the Amazon forests could react drastically”, though one might quibble with Nepstad’s assertion that it substantiated the words about this being the result of “even a slight reduction in precipitation”. In the context of the IPCC’s word “could”, maybe it does. […]

I agree I could have been harder on the IPCC at this point. I have no desire either to support or denigrate the IPCC text which, I suggest, might have been better composed. In any event, I wished to save my criticism for rather more clear-cut indiscretions.

It got the references all wrong for a claim that 40 per cent of the Amazon rainforest could die within a few decades from heat and drought. Sloppy again, but no big deal. (emphasis not in original)

3) In a fresh article in the Yale Environment 360 website about climate models

But other errors were failures to articulate uncertainties. The study highlighted a claim that even a mild loss of rainfall over the Amazon could destroy 40 percent of the rainforest, though only one modeling study has predicted this.

Why is Pearce wrong?

It is evident what Pearce is doing, is a slow de-escalation of how shaky the IPCC’s Amazon claims are. The basis for these three claims from Pearce, if you can call it that, is found in the interview with Roger Pielke Jr. Pearce seems to be of the view, after just reading the references provided by Dan Nepstad that the “correct claim-wrong citations” excuse still has feet to stand on.

Nepstad et al, 2004 is a study reporting on a computer model examining the risk for forest fires but the IPCC WG II statement on the Amazon is not about computer model outputs. Herein we arrive at a peculiar problem created by the ‘citation-spraying fog of academic war’ effect that we saw with Amazongate. The IPCC statement has been by turns, erroneously propped up the savannization/dieback literature cited by Simon Lewis and his long complaint letter and the Woods Hole Research Center press release, and by Nepstad and his fire-risk papers. How are both possible at the same time?

Nepstad 2004 assumes a 75% soil water deficit will produce a 25% reduction in canopy cover over the entire Amazon system. Stemming from that assumption, in the computer model sunlight purportedly dries the forest floor wherein lie all the fallen leaves, setting off fires.

In Nepstad 2004, 40% of forest is modeled, by extrapolation of soil moisture content estimation, to be susceptible for canopy loss. Depletion of water up to 5 meters depth is assumed to trigger leaf loss and this then is supposedly exposes the forest floor, increasing ‘fire risk’. The number (40%) is derived for one of the years studied and thus does it come about that ‘40% of the forest” is at “at risk for fire”, This is the specific, limited meaning and origin of the 40% number. It is not the extent of forest that would flip/die/fall off with a slight reduction of rainfall.

It has therefore, no connection with how it has been used in the IPCC. Yet it is supported by proponents of a different paradigm – the savannization paradigm, by Simon Lewis, – by George Monbiot in his Guardian article and now Pearce citing Cox et al 2004 – simply because both schools of thought share one thing. And that is, a suitably high magical number – 40%.

Two different concepts, two different lines of thought, and the literature underlying them – gets used interchangeably, simply because they seem to support a single concept of catastrophic forest loss in the Amazon.

That Pearce uses this same peculiar breed of scientific and citation logic is enough to see that he is wrong.

There are other problems here as well, we will only note in passing. The somewhat unique style of stringing suppositions and extrapolations observed in Nepstad 2004 is seen in another study of Amazonia Nepstad et al, 2008 as well, where an alarming 55% of the entire Amazon is ‘lost’ by computer-modeling in the next 20 years, due to various influences.

Further surprises

What is furthermore surprising? It appears that the Nepstad-derived forest canopy loss driven fire-risk paradigm cannot be supported with presently available literature. Recent literature from remote sensing studies show that the period of leaf flush is precisely the same dry period during which moisture depletion occurs, in tropical systems like the Amazon. This is the exact opposite of the basic assumption underlying estimates derived from Nepstad et al 2004.

Upper soil dryness, being coincident with canopy green-up, strikes at the very cornerstone of the ‘Nepstad-IPCC-IPAM cartoon’ paradigm. A similar ‘paradoxical’ forest response is seen in tropical forests in Hawaii ( Pau et al, 2010), India and Thailand (Borchert 2006) as well. Undisturbed, unlogged forest canopy stays intact in the regular ‘summers’, and even the worst of dry periods (Saleska et al, 2007, Samanta et al, 2010) in the Amazon, even as other indices of tree mortality are affected (for eg, see Philips et al, 2009). One thing ought to be clear here – what these results mean, for the forest as a whole responding to drought is something different and is actively being studied (Brando et al, 2010, Anderson et al, 2010).

What we can be reasonably certain however is is that tropical forests don’t simply flip or burn away even in prolonged droughts, via the ‘cartoon pathway’, simply because their physiology is flipped already to begin with.

Satellite generated map of EVI of Amazonia (C) NASA Earth Observatory

As for Nepstad et al, 2007, one only needs to carefully look at how this study is understood in the Amazon fire risk literature to realize how off the mark Pearce is. For example, Barlow et al, 2008 are of the clear view that Nepstad’s 4-year experimental drought findings reported in 2007, only establishes that “Amazonian forests appear to be more resilient to drought stress than previously thought”. The mere fact that such a prolonged drought simulation is hardly the same as a “small reduction in rainfall” seems to be lost on Pearce as well.

Another key fact overlooked by Pearce, is that the website and the WWF report (Global Review of Forest Fires) made claims about the Brazilian Amazon, which the IPCC simply extrapolated to the entire Amazon system. A 40% fraction of these two are completely different from each other – but then again, such small facts have been forgotten time and again, in this byzantine debate.

What do we make of this then?

One explanation is that, Pearce wants to tell us, as appears to be his wont, that only his glacier exposé is any good at all, in the saga of errors and exaggerations uncovered in the IPCC AR4.

The larger picture though is – there is a need to get the Amazon-REDD agenda back on its feet so it hobbles over to the finish line by 2012. Let us hope Pearce knows that his exonerations will provide a way for the discredited Amazongate alarmism to get up back on its feet again.

Related

3 comments

It’s probably fair to point out that the WWF report which I believe was called “Global Review of Forest Fires” and which was one of the IPCC citations, never pretended to be anything else than a discussion of fires. It was not a general discussion of loss of forest due to changes in rainfall, I’ll quote:

“Up to 40% of the Brazilian forest is extremely sensitive to small reductions in the amount of rainfall. In the 1998 dry season, some 270,000 sq. km of forest became vulnerable to fire, due to completely depleted plant-available water stored in the upper five meters of soil.”

Note that the IPCC upgrades “40% of the Brazilian forest” to pretend it is 40% of the whole Amazon, and then further upgrades “vulnerable to fire” up to a presumption that all vulnerable areas will convert to savannah. The IPCC carefully skips over any discussion of fires, or the important point that most forest clearing (by fire and other means) is deliberate, initiated by humans for the purpose of making more agricultural land (which is a point that the WWF report does cover).

As you say, “two different concepts, two different lines of thought” but the WWF was far more faithful to the original research than the IPCC have been.

About the two different lines of thought:
The first one is the damage from fire to the Amazon. The second is the dieback theory put forth by Nobre, Cox and his Exeter modeling group.

The IPCC, as you note, used a passage pertaining to Amazon fires, but implying ‘climatic damage’. They cleverly failed to mentioned what exactly the ‘drastic changes’ were, in using the WWF passage.

Nepstad, of course has argued that the risks of climate change are ‘mediated by fire’ in the Amazon. That was the one of the many link Amazon researchers have tried to provide between their original work and climate change.